Gunmen shot up a police helicopter that helped chase a driver who fled a traffic stop in Puerto Rico, mortally wounding one crewman and injuring the second, an FBI official said Wednesday.

The San Juan municipal police officer died Wednesday of wounds suffered in the shooting late Tuesday, FBI spokesman Harry Rodriguez said.

Rodriguez said the FBI had assumed jurisdiction over the case following discussions with the U.S. island's police chief.

"In accordance with the guidelines established by the U.S. Department of Justice this is a death penalty eligible case," the spokesman said.

The helicopter was following the driver who sped away from officers on the ground in Rio Piedras, outside Puerto Rico's capital, San Juan.

As police closed in and arrested the suspect, a group of men nearby opened fire on the helicopter, firing at least 31 bullets and hitting the officers on board, local police spokesman Eduardo Rodriguez said. He said the pilot made a forced landing in a baseball field.

Eleven people were detained by police for questioning but all had been released, the FBI spokesman said. He said nobody was in custody in the case.